Thermoplastic materials are commonly used in the packaging of various products including food products. Often these materials are processed to provide a heat shrinkable film. One distinguishing feature of a heat shrink film is the film's ability, upon exposure to a certain elevated temperature, to shrink or, if restrained from shrinking, to generate shrink tension within the film. Shrink films may be manufactured by extrusion or coextension of thermoplastic resinous materials which have been heated to their flow or melting point from an extrusion or coextrusion die in, for example, either tubular or planar form. After a post-extrusion quenching to cool by, for example, the well known cascading water method, the relatively thick "tape" extrudate is then reheated to a temperature within its orientation temperature range and stretched to orient or realign the molecules of the material. Orientation temperatures will vary with the type of polymer which comprises the material, but is generally below the crystalline melting point of the material and above the second order transition temperature (glass transition temperature) thereof. Stretching of the material by tenter framing or the well known bubble process may be employed. A stretching force may be applied in one direction (uniaxial) or two directions (biaxial). An oriented, i.e. heat shrinkable material will tend to return to its original unstretched dimensions when heated to an appropriate elevated temperature.
Thus shrinkable films are specially suitable for the packaging of many food products.
It is often also desirable to include a layer of barrier material within the above formulation to provide good oxygen and/or vapor barrier characteristics to the resulting package. The end use of the package may require a low permeability to either oxygen, water vapor, or both to maintain the freshness of the food contained therein.
Food products such as specialty cheese are commonly packaged in the store, at point of sale. Typically, these food products and specialty items are hand wrapped, costing time and expense for the seller. The packaged product itself usually has a shelf-life of only a few days.
It is therefore desirable to provide pre-packaged products, such as specialty cheeses and the like, which do not require costly in-store packaging or repackaging. It is also desirable to provide a package with the look and configuration of an in-store wrapped item, in order to increase consumer appeal for the packaged item.
The present invention provides a package and process allowing for pre-packaging of food products, and utilizing a shrinkable, barrier material which provides a tight, close-fitting package with an extended shelf-life.
Of interest is U.S. Pat. No. 2,545,243 issued to Rumsey. This patent discloses a method to provide for the escape of air from the inside of a package as a plastic sheet material is secured and tightened around the package. A thermoplastic film, preferably heat shrinkable is overlapped and underlain with a parchment paper or similar material directly against the food product to be packaged. Apertures are created at several points in the overlapped layers of the packaging material, with the overlapped layers themselves being fused in the areas immediately surrounding the apertures. After closure of the package, the apertures allow entrapped air to escape during heating of the thermoplastic material in hot water to cause additional shrinking of the package. Although this reference provides for a tight casing for food products, it relies on parchment paper or similar material directly against the food product and beneath the aperatures of the overlapped areas of the package to protect that food product. This reference also requires reliance on the spiral twisting of the ends of the package to remove some of the entrapped air, followed by shrinking of the packaging material about the product to remove any wrinkles or looseness about the product.
Also of interest is U.S. Pat. No. 3,026,656 issued to Rumsey and disclosing a package for meat and dairy products and the like. A heat shrinkable, heat sealable material is preferably used. Apertures are introduced into the film so as to be offset with respect to overlapping edge portions of the film. Suction is applied to the outer surface of the overlapping layers to withdraw the entrapped air inside the package through the inner aperture, between the overlapping layers, and finally outwardly through the outer aperture. While suction is maintained, the overlapping layers are sealed together to prevent reentry of air, and the thermoplastic material is heat shrunk around the package. This method has a disadvantage of requiring careful overlapping of the film to ensure proximately spaced apertures, and also requires a separate vacuum step to draw the entrapped air from inside the package prior to the heat shrinking step.
It is an object of the present invention to provide a package and a method of packaging of food products such as cheese and the like whereby entrapped air may be withdrawn from the inside of a package without the need for vacuumization of the package.
It is also an object of the present invention to provide a package and a method of packaging food products such as cheese and the like without the need for twisting of the ends of the package to remove the entrapped air from the package through one or more apertures.
It is a further object of the present invention to provide a package and method of packaging of food products such as cheese and the like without the need for gas flushing of the packaging prior to sealing and shrinking of the packaging material.